ezusb_read_ltv() is always invoked via the ->read_ltv() callback. This
callback is mostly invoked under orinoco_lock() which disables BH.

There are a few invocations during probe which occur in preemptible
context via:
   ezusb_probe() -> orinoco_init() -> determine_fw_capabilities()

Extend `hermes_ops' with the ->read_ltv_pr callback which is implemented
with the same callback like ->read_ltv on `hermes_ops_local'.
On `ezusb_ops' ->read_ltv is used for callbacks under the lock which
need to poll.
The new ->read_ltv_pr() is used in the preemptible context in which it
is possible to wait for the completion. Provide HERMES_READ_RECORD_PR()
and hermes_read_wordrec_pr() which behave like their non _pr equivalents
and invoke ->read_ltv_pr().

This removes the last user of ezusb_req_ctx_wait() and can now be
removed.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201113212252.2243570-11-bigeasy@linutronix.de